The present invention relates to a method, apparatus and program for alarming abnormality in tire air-pressure.
A method for alarming abnormality in tire air-pressure in accordance with the prior art in which a decrease in tire air-pressure is detected and an alarm is issued, makes use of a fact that a tire having a decreased tire air-pressure rotates faster than a tire having a normal tire air-pressure. The method for alarming abnormality in tire air-pressure detects whether or not an air-pressure in tire is decreased based on the variation of a determinate value (DELL) calculated from a rotational velocity of each tire by the following equation, and issues an alarm when it is determined that the air-pressure in any tire is decreased. In the following equation FL, FR, RL and RR represent a rotational angular velocity of the front left tire, the front right tire, the rear left tire, and the rear right tire, respectively.DEL1=((FL+RR)/(FR+RL)−1)×100, or((FL+RR)−(FR+RL))/(FL+FR+RL+RR)×200
However, when a vehicle runs after replacing with a new tire, the rotational velocity of the new tire decreases due to an enlargement of the diameter of the new tire. As a result, in the method for alarming abnormality in tire air-pressure in accordance with the prior art there has been a case where an erroneous alarm is issued or alarm is not issued at all when the new tire is mounted on a vehicle.
In Japanese Unexamined Patent Publication No. 211220/2002, a tire discrimination apparatus and method for having a capability to discriminate a kind of tire mounted on a vehicle replacing a different kind of old tire by an initialization process, to improve accuracy of determination of a decrease in tire air-pressure, and to prevent giving an erroneous alarm or no alarm and an apparatus and method for alarming decrease in tire air-pressure with the use of the above apparatus are issued. However, that invention does not teach a method to prevent issuing an erroneous alarm or no alarm when a new tire is mounted in place of an old tire.